Posted by GregSeaHawk on
URL: https://forum.seahawk17.org.uk/engine-size-tp4023996p4024006.html

Hi Peter,

Apologies for a lack of any earlier response!

Given the physics of displacement hulls, ( http://en.wikipedia.org/wiki/Hull_speed ) speed of current in flat water should not be the issue to be concerned about, because a SeaHawk will never manage to beat anything much more than a 6 knot current.

The reason you may need something beefier than 1.5hp (the original inboard engine power that was fitted to SeaHawks) is waves. Bare in mind that hull speed calculations assume horizontal water. The lowest power engine, given an appropriate prop, even my little electric motor with just 50lbs of thrust, is capable of pushing a SeaHawk through level water at its hull speed.

The reason why you may need something with more grunt is pushing the full weight of boat, crew and provisions, up waves. That's where a less powerful engine will begin to struggle.

There are a good number of people who use 2.5hp engines and swear by them - but they are frequently Broads-based where there are no waves to speak of.

It all depends on whether you feel you need to be prepared to encounter significant wind against tide effects or other wave-inducing conditions as to whether you need the comfort of knowing you have the grunt available to fight waves. Current is another matter. You may never beat that in full flood.